The present invention generally relates to automatic volumetric dispensing systems, and particularly relates to a system and method for dispensing different volumes of a toxicant or other fluid test material to a plurality of vessels.
It will be readily appreciated that it is desirable to test or evaluate environmental effects of chemical toxicants and other test materials on marine or aquatic organisms. One of the principal methods that toxicologists use to predict the potential environmental effects of synthetic chemicals, such as toxicants, is the direct exposure of specimens of a selected test species to a graduated series of dosages of the particular chemical or other test material of interest. When the test species or organisms are from marine or aquatic environments, the test material dosages are typically applied as a graduated series of concentrations in water. These concentrations are ideally maintained at exactly the same levels in the test vessels containing the organisms throughout the duration of the test. To approach this exactitude of concentration, it is necessary to continually or periodically supply fresh, properly diluted quantities of the fluid or suspended test material to compensate for losses of this material in the vessels containing the organism specimens. These losses are due to such factors as volatilization, absorption, decomposition, biological uptake, and other similar removal processes.
Thus, it is necessary to replenish the supply of the toxicant or test material in the vessels in order to maintain a stable concentration of the test material in each of the vessels. Typically, this replenishment procedure involves a dispensing cycle in which each of the vessels is supplied with a fixed volume of a solution containing the test material, a dilution fluid (e.g., water), and sometimes a carrier liquid. Each vessel or group of vessels is given a different concentration of the test material in order to determine the effect of the test material on the organisms at these different concentration levels. The groups of vessels referred to previously, are duplicates in the context of standard scientific procedures. In this regard, it is generally desirable for the toxicologist to prepare a dose response curve which graphs the effect of the varying concentrations of the test material on the organisms. From this curve, the toxicologist can predict the concentration of the test material which will produce a median lethal dosd (LC 50) and a no observable effect level (NOEL) upon the organism being studied. Since the accuracy of the dose response curve is dependent upon the number of different concentrations for the test material being evaluated, it is generally desirable to provide a dispensing system which is capable of providing a multitude of different concentrations as required to produce an accurate and reliable curve. It is desirable that a single dispensing system be used because it eliminates the error which could be introduced if two or more dispensing systems were employed which were not exactly matched and calibrated in terms of thier operational characteristics.
Systems to accomplish this tedious dilution and supply function are generally known in the art as diluters. One of the most common diluter designs used by toxicologists is a gravity-fed system of reservoirs and siphons which is based upon the Mount and Brungs design disclosed around 1960. With this design, there is a practical limitation on the number of different concentrations that can be provided, because the proportional ratio of concentrations is set by the physical equipment, such as the size of the vessels. In this regard, the upper limit is generally considered to be ten different concentrations per diluter with a maximum ratio highest to lowest concentration of 10:1. Additionally, this diluter design exposes the toxicant to the atmosphere, since siphon action or gravity flow is used to cause the flow of the toxicant from one level of vessels to the next to produce the varying concentrations of the toxicant. As a result, test toxicants which are volatile and/or sensitive to air are often compromised. The design constraints of this type of diluter usually accentuate any tendency that toxicants may have to separate and settle or rise to the surface (e.g., emulsions). Additionally, due to the fact that only gravity pressure is being used, sufficient velocity is not generated to sweep the inner walls of the toxicant conveying tubes clean and thusly, significant toxin loss may occur due to inner wall accretion. In order to clean this kind of proportional diluter, it is almost always necessary to completely disassemble the system between tests.
Another significant limitation of the above described gravity-fed diluter design, as well as other proportional diluter designs, is the lack of the ability to independently set toxicant and dilution fluid volumes. In these designs, there is a direct proportional relationship between the volume of the toxicant and the volume of the dilution fluid in each of the vessels. These proportional relationships are fixed by the physical sizes of the vessels employed in the design. Accordingly, in order to change the range of concentrations employed for a test, it is necessary to change the physical hardware in the diluter system. Additionally, the only way to change the highest concentration is to change the stock solution concentration of the toxicant. Further, calibration and other fine adjustments to such proportional diluters involve physically moving siphon or drain tubes up and down in a trial and error procedure. Each adjustment requires one or more compensatory adjustment in other vessels feeding that particular concentration, a difficult and often inaccurate procedure at best.
Another known diluter design is referred to as a positive displacement diluter. Positive displacement diluters use positive displacement pumps to simultaneously measure and pump the toxicant and dilution fluid. The measurement is made by counting the number of strokes or revolutions for both the toxicant pump and the dilution fluid pump. However, this diluter design also has significant limitations, such as the need to lubricate the pump's pistons or rotors without contaminating the fluids being pumped. Other such limitations include the existence of a dead period in the lines between strokes of the pumps and the need for mechanical valves that can clog or leak backward thus altering the delivered volume. There are also mechanical limitations on the number of different concentrations. In this type of diluter design, it is very difficult to provide for a large number of concentrations while simultaneously providing acceptable accuracy for the study. Close mechanical tolerances are generally required, and this makes it difficult for the diluter to dispense test materials which have suspended particulates (e.g., abrasive materials). The required close tolerances and the complexity of these diluters often leads to maintenance problems which are unacceptable for tests which involve long-term chronic exposures of the test material to the organisms.
Additionally, even though positive displacement diluters are more versatile than proportional diluters, positive displacement designs are also quite limited in the range of test material concentrations that can be delivered, as these designs typically require mechanical changes to provide a concentration which is more than a factor of ten from another concentration level. It should also be noted that these systems generally cannot be fine tuned to adjust for minor deviations of individually delivered concentrations from the concentration levels required by the testing protocol.
One system that has not been used as a diluter but does have the capability of volumetrically combining various fluid streams is made by Technicon Instruments Corp. (35 Benedict Ave., Terrytown, N.Y. 10591) and is used primarily for automated chemical analysis. The system uses a bank of peristaltic pumps on a single shaft and varies the volume delivery by varying the bore size of the pump tubing. This greatly limits its range of delivery volumes and makes calibration of individual pumped streams virtually impossible. The system also suffers from the usual shortcomings of peristaltic pumps such as back flow of fluid, tubing fatigue and breakage, and delivery volume changes due to progressive changes in tubing geometry.
It is also worthy to note that the test materials which often attract the most scientific interest are those which have very low solubilities in water (e.g., typically less than one milligram per liter). Prior diluter designs, whether of the proportional or positive displacement types, are generally limited in their ability to mix the test material and dilution water in the precise quantities necessary to provide an accurate test for these very low solubility test materials. Also, all of the prior diluter systems were limited to a specific distribution sequence relative to the concentration levels to be placed within the vessels. That is, the prior systems distributed their substances in a sequence ranging from the highest to the lowest concentrations or vice versa. This linear sequence allows such non-experimental variables as toxicant supply tube length unavoidable longitudinal temperature gradients in the water bath containing the test vessels, and other large-scale conditions to affect test results. Such variation patterns could theoretically be statistically eliminated if test vessel concentrations could be randomized, thus greatly improving the data quality.
Accordingly, it is a principal object of the present invention to provide an automatic diluter system for dispensing different volumes of a fluid test material to a plurality of vessels which overcomes many of the limitations of prior diluter designs.
It is another object of the present invention to provide a diluter system in which the variations in concentration are no longer dependent upon mechanical constraints, but may be readily affected through computer software programming changes.
It is a further object of the present invention to provide a diluter system which is capable of handling a high number of different concentrations of the test material in a single test.
It is an additional object of the present invention to provide a diluter system which has the ability to independently set test material and dilution fluid volumes.
It is also an object of the present invention to provide a diluter system which has the ability to handle very low solubility toxicants, and the ability to handle volatile toxicants through the use of isolation from the atmosphere and short transfer times.
It is yet another object of the present invention to provide a diluter system which has the capability of randomizing the order in which the different concentration volumes are delivered to their respective test vessels during different tests in order to improve statistical parameters.
It is yet an additional object of the present invention to provide a diluter system which has a provision for automatically washing the pipelines after a test has been concluded to substantially decrease the turnaround time required between tests.
It is yet a further object of the present invention to provide a diluter system which has the ability to control the temperature of the fluids being conveyed to improve the reliability of test results.
It should be noted that most of the design objectives that this computerized diluter achieves are identical to the needs of several other fields and thus represent direct applications of this design. In general, continuous flow production and fabrication processes are inherently advantageous over batch processing methods but have not been achievable due to the unavailability of reliable continual-flow type ingredient mixing equipment, that is: volumetrically accurate over a wide range of flow rates; can handle many ingredients simultaneously; can dispense a wide range of mixture ratios including trace quantity ingredients; is easy to set up and adjust; is volumetrically stable; can handle viscous fluids, emulsions, foams and suspensions; provides temperature control; will be self monitoring and provide alarms and help requests; is self cleaning; can be programmed flexibly; and is constructed primarily of widely available components. All these and more are achievable with the computerized volumetric dispensing system of this invention. This system may be used in such applications as providing food ingredient mixtures to tube ovens and extrudes, feeding reactant charges to continuous flow chemical reators, or providing the mixture of monomers, colorants, antioxidants and other ingredients to plastic extrudes and sequential molding operations.